Modelling of enzymatic reaction in an internal loop airlift reactor

Gas-liquid reaction carried out in an internal loop airlift reactor was modelled and subjected to the scale-up procedure. Homogeneous oxidation of glucose to gluconic acid catalyzed by Gluzyme 10000 BG, a commercial product containing the enzymes glucose oxidase and catalase as active components, was chosen as the model system. The kinetic parameters were obtained using a 12-L airlift reactor considered as a CSTR. The behaviour of a large-scale internal loop airlift reactor was modelled dividing the reactor sections into a series of tank reactors. The reliability of the model was verified by comparing experimental measurements with the simulation results obtained employing 40-L and 200-L airlift reactors. The designed model could be suitable to predict the behaviour of large-scale internal loop airlift reactors. Presented at the 33rd International Conference of the Slovak Society of Chemical Engineering, Tatransk%e Matliare, 22–26 May 2006.     

Modeling of enzymatic reaction in an airlift reactor using an axial dispersion model

This work was focused on modeling of biochemical processes in a 40-L internal-loop airlift reactor. Due to different mixing in the specific zones of the reactor four main sections, bottom, riser, separator and downcomer, were recognized. Each zone was modeled by an adequate mixing model: bottom and separator sections by the model of ideally-stirred reactor; riser and downcomer sections by the model of plug-flow reactor with axial dispersion. In the model, the effects of mass transfer, hydrodynamics, and reaction kinetics were taken into account. The model of the reactor was experimentally verified by the aerobic enzymatic oxidation of glucose to gluconic acid. Simulations are in good agreement with experimental data. Presented at the 34th International Conference of the Slovak Society of Chemical Engineering, Tatranské Matliare, 21–25 May 2007.     

Effect of the shear rate on pullulan production from beet molasses by Aureobasidium pullulans in an airlift reactor

The effect of the shear rate on pullulan production from beet molasses by Aureobasidium pullulans P56 in an airlift reactor was investigated. A maximum polysaccharide concentration (18.5 g/L), biomass dry weight (14.0 g/L), polysaccharide yield (38.5%), and sugar utilization (96%) was achieved at a shear rate of 42 s⁻¹. A. pullulans grown on beet molasses produced a mixture of pullulan and other polysaccharides. The highest value of pullulan proportion (30% of total polysaccharide) was obtained at a low shear rate (42 s⁻¹). The apparent viscosity of the fermentation broth increased as the shear rate increased up to 42 s⁻¹ and then decreased. On the other hand, the dissolved oxygen concentration and the volumetric mass transfer coefficient increased with the increase of the shear rate from 21 to 84 s⁻¹. The external addition of L-glutamic acid, olive oil, and Tween-80 improved significantly the production of crude polysaccharide (27.0 g/L), but the pullulan content of the polysaccharide was low (20%).     

Influence of temperature on performance of an anaerobic sequencing biofilm batch reactor with circulation applied to treatment of low-strength wastewater

The effect of temperature on the performance of an anaerobic sequencing biofilm batch reactor (ASBBR) with liquid-phase recirculation was assessed. Assays were performed using a recirculation velocity of 0.20 cm/s, 8-h cycles, and an average treated synthetic wastewater volume of 2 L/cycle with a concentration of 500 mg of Chemical Oxygen Demand (COD)/L. Operation temperatures were 15, 20, 25, 30, and 35°C. At 25, 30, and 35°C, organic matter removal efficiencies for filtered samples ranged from 81 to 83%. At lower temperatures, namely 15 and 20°C, removal efficiency decreased significantly to 61 and 65%, respectively. A first-order model could be fitted to the experimental concentration profile values. The first-order kinetic parameter value of this model varied from 0.46 to 0.81 h¹ considering the lowest and highest temperature studied. Moreover, analysis of the removal profile values allowed fitting of an Arrhenius-type equation with an activation energy of 5715 cal/mol.     

Performance of an internal-loop airlift bioreactor for treatment of hexane-contaminated air

Hexane is a toxic volatile organic compound that is quite abundant in gas emissions from chemical industries and printing press and painting centers, and it is necessary to treat these airstreams before they discharge into the atmosphere. This article presents a treatment for hexane-contaminated air in steady-state conditions using an internal-loop airlift bioreactor inoculated with a Pseudomonas aeruginosa strain. Bioprocesses were conducted at 20-mL/min, a load of 1.26 g/m³ of C₆H₁₄, and a temperature of 28°C. The results of hexane removal efficiencies were presented as a function of the inoculum size (approx 0.07 and 0.2 g/L) and cell reuse. Bioprocess monitoring comprises quantification of the biomass, the surface tension of the medium, and the hexane concentration in the fermentation medium as well as in the inlet and outlet airstreams. The steady-state results suggest that the variation in inoculum size from 0.07 to 0.2 g/L promotes hexane abatement from the influent from 65 to 85%, respectively. Total hydrocarbon removal from the waste gas was achieved during experiments conducted using reused cells at an initial microbial concentration of 0.2 g/L.     

Continuous fast pyrolysis of biomass at high temperature in a fluidized bed reactor

In order to perform biomass pyrolysis a continuous fluidized bed reactor (bench scale unit) has been assembled. The influence of experimental conditions such as heating-up time and optimum particle diameter is presented. By feeding the biomass (almond shells) directly into the bubbling bed, pyrolysis has been performed at temperatures ranging from 730° to 930°C at constant feed rate (44 g/h). Remarkable increase of H₂ in the product gas is observed when steam rather than an inert carrier such as nitrogen is used thus confirming the potential of this approach.The support of ENEA (Italian Agency for Renewable Energies) is gratefully acknowledged.     

Continuous production of antibiotics in an airlift fermentor utilizing a transverse magnetic field

In this study, a series of experiments was conducted to demonstrate the feasibility of continuous production of penicillin antibiotic using a three-phase magneto airlift fermentor with immobilized Penicillium chrysogenum. The fermentation processes were carried out in a 2.4-L external loop airlift utilizing a transverse magnetic field. It was found that the application of the magnetic field to a bed of ferromagnetic beads affects both the hydrodynamics of the reactor and the rate of the bioconversion process occurring inside it. One hundred hours after startup, the maximum penicillin concentration increased 48% as the magnetic field intensity increased from 0 to 35 mT, owing to the increased residence time of the substrate in the riser and the positive effect of the magnetic field on the effective fluid-solid interfacial area. In addition, the detached biomass concentration in the liquid phase was found to be only 5% of the immobilized biomass, owing to low shear levels and the absence of friction among the solid-phase particles.     

Flow field in a shrinking-bed reactor for pretreatment of cellulosic biomass

A shrinking-bed reactor was designed by the National Renewable Energy Laboratory to maintain a constant bulk packing density of cellulosic biomass. The high solid-to-liquid ratio in the pretreatment process allows a high sugar yield and avoids the need to flush large volumes of solution through the reactor. The shrinking-bed reactor is a promising pretreatment reactor with the potential for scale-up for commercial applications. To scale up the shrinking-bed reactor, it is necessary to understand the flow pattern in the reactor. In this study, flow field is simulated with computational fluid dynamics using a porous medium model. Different discrete “snapshots” and multiple steady states are utilized. The bulk flow pattern, velocity distribution, and pressure drop are determined from the simulation and can be used to guide reactor design and scale-up.     

Two-temperature modeling of an arc plasma reactor

In this paper a two-temperature plasma model is established and applied to the injection of cold gases into an atmospheric-pressure, high-intensity argon arc. The required nonequilibrium plasma composition and the non-equilibrium transport properties are also calculated. The results show that the arc becomes constricted at the location of gas injection due to thermal and fluid dynamic effects of the injected cold flow. Enhanced Joule heating in the constricted arc path raises the electron as well as the heavy-particle temperatures. This temperature increase resists, via secondary effects, the penetration of the cold gas into the hot arc core which behaves more or less as a solid body as far as the injected flow is concerned. The temperature discrepancy between electrons and heavy particles is most severe at the location of cold flow injection, a finding which may have important consequences on chemical reactions in an arc plasma reactor.     

Depolymerization of xylan-derived products in an enzymatic membrane reactor

Rice husks were subjected to aqueous processing to obtain liquors containing xylan-derived products, which were assayed for composition. Liquors were diafiltered using 1 kDa ceramic membrane for purification purposes, and the retentate was concentrated using the same membrane. The molecular weight distribution of xylan-derived products in concentrated liquors was assayed by gel permeation chromatography. In order to achieve the one-step conversion of soluble, high molecular weight xylan-derived products into low molecular weight arabino-xylooligosaccharides (AXOS) and the recovery of low molecular weight AXOS, concentrated liquors were treated in a continuous enzymatic membrane reactor (EMR) with a commercial endoxylanase (Shearzyme 2X). Two operational modes were studied: in the first one, both enzymatic reaction and membrane operation began at the same time, whereas in the second case, permeation started when the reaction achieved a given conversion. Both operational modes are compared in terms of productivity.     

Antimicrobial secondary metabolites of an endolichenic Aspergillus niger isolated from lichen thallus of Parmotrema ravum

Abstract

A new 6-benzyl-γ-pyrone (1), named aspergyllone was isolated from the culture filtrates of an endolichenic fungus Aspergillus niger Tiegh, obtained from lichen thallus Parmotrema ravum (Krog & Swinscow) Serus, collected in India. 1 was isolated for the first time from an endolichenic fungus together with six other known metabolites identified as aurasperones A (2) and D (3), asperpyrone A (4), fonsecinone A (5), carbonarone A (6) and pyrophen (7). The compounds were tested against a panel of human, plant, food borne and fish pathogens. Aspergyllone showed strong selective antifungal activity against Candida parapsilosis (Ashford) Langeron & Talice, with an IC₅₀ of 52?µg/mL. Aurasperone A and pyrophen showed moderate to strong antimicrobial activity inhibiting seven different test pathogens, being pyrophen active with IC₅₀ ranging from 35 to 97?µg/mL.

     

Design of two-stage membrane reactor for the conversion of coke-oven gas to H2 and CO

The catalyst function was achieved in two regions in an oxygen permeation membrane reactor： H2 dissociated and reacted with lattice oxygen or oxygen ions to form H20 near the membrane surface. The H20 formed could react with the residual CH4 away from the membrane surface area.     

Development of continuous surfactin production from potato process effluent by Bacillus subtilis in an airlift reactor

The biosurfactant surfactin has the potential to aid in the recovery of subsurface organic contaminants (environmental remediation) or crude oils (oil recovery). However, high medium and purification costs limit its use in these high-volume applications. In previous work, we showed that surfactin can be produced from an inexpensive low-solids (LS) potato process effluent with minimal amendments or pretreatments. Previous research has also shown that 95% or more of the surfactin in Bacillus subtilis cultures can be recovered by foam fractionation. In this work, we present the results of research to integrate surfactin production with foam fractionation. Experiments were performed in an airlift reactor, with continuous collection of the foam through a tube at the top of the column. Preliminary results using both purified potato starch and unamended low-solids potato process effluent as substrates for surfactin production indicate that the process is oxygen limited and that recalcitrant indigenous bacteria in the potato process effluent may hamper continuous surfactin production.     

The chemical reduction of small inorganic gases in an electrothermal plasma reactor

Chemical reduction of small inorganic gases is accomplished using an electro-thermal plasma reactor. This benchscale reactor maintains a highly reactive plasma zone in a fluidized bed of carbon particles through which an electrical current is discharged. The carbon particles function as current-controlling media, heat sinks and reaction sites. Chemicals introduced into this medium are subjected to a variety of energy sources and chemically reactive species, which result in chemical reduction. It is shown that the inorganic gases, H₂O, CO₂, NO, NO₂ and SO₂, are chemically reduced in the plasma zone of the reactor. The end products consist of hydrogen, carbon monoxide and nitrogen gases. Additionally, elemental sulfur is deposited onto the carbon particles.     

Determination of l-alanine in a flow-injection system with an immobilized enzyme reactor

A flow-injection system for the determination of l-alanine is described. Alanine dehydrogenase is immobilized on poly(vinyl alcohol) beads and used in a packed-bed enzyme reactor. The system responds linearly to injected samples (50 μl) in the concentration range 0.5–500 μM. The maximum throughput was 40 samples per hour. The immobilized enzyme reactor was stable for at least 6 weeks. Its usefulness for assay of l-alanine in serum and beverages is described.     

The use of an immobilized enzyme nylon tube reactor incorporating a four enzyme system for creatinine analysis

A single immobilized enzyme nylon tube reactor was produced incorporating a four enzyme system for the analysis of creatinine. The enzyme activity ratios in the coupling solution used to prepare the reactor were found to be of extreme importance in governing the activity of the latter. The reactor was incorporated into a continuous flow analysis system used to assay creatinine in urine samples and the results were correlated with a manual technique employing the same enzyme system in solution. The precision, correlation, high specificity, simplicity, and speed of the analysis were concluded to be factors in favor of the method's suitability for urine creatinine determinations.     

Comparison between the performance of an immobilized impinging jet stream reactor and a slurry impinging jet stream reactor for photocatalytic phenol degradation

A new immobilized photocatalytic impinging jet stream reactor was designed, and the influences of the effective parameters like jet flow rate, TiO₂ coating disc diameter, nozzle-to-disc distance, and initial concentration on phenol removal were investigated. The reactor was also used as a slurry reactor, and degradation efficiencies in both reactors were compared based on their catalyst loading. The results indicated that the slurry reactor has a higher degradation efficiency than the immobilized reactor at the same TiO₂ loading and other operational conditions. The slurry reactor needs to separate and recover the TiO₂ nanoparticles from the reaction medium which increases the overall process complexity and cost, while the immobilized reactor could be reused at least 4times without any significant decrease in removal efficiency. RTD result indicates that the tank in series model (N?=?5) could properly predict the reactors hydrodynamic behavior.     

Flow-injection system for the fluorimetric determination of fructose with an immobilized mannitol dehydrogenase reactor

Immobilized mannitol dehydrogenase is used for the determination of D-fructose in a flow-injection system. The enzyme is immobilized on poly(vinyl alcohol) beads. The oxidation of NADH occurs simultaneously and the disappearance of NADH is measured fluorimetrically. The response is linearly related to fructose concentration in the range 6–600 μM; 30 samples per hour can be analysed. The immobilized enzyme retains over 80% of its initial activity after repetitive use for 2 months.     

Development of an open-tubular trypsin reactor for on-line digestion of proteins

A study was initiated to construct a micro-reactor for protein digestion based on trypsin-coated fused-silica capillaries. Initially, surface plasmon resonance was used both for optimization of the surface chemistry applied in the preparation and for monitoring the amount of enzyme that was immobilized. The highest amount of trypsin was immobilized on dextran-coated SPR surfaces which allowed the covalent coupling of 11 ng mm⁻² trypsin. Fused-silica capillaries were modified in a similar manner and the resulting open-tubular trypsin-reactors having a pH optimum of pH 8.5, display a high activity when operated at 37 °C and are stable for at least two weeks when used continuously. Trypsin auto-digestion fragments, sample carry-over, and loss of signal due to adsorption of the protein were not observed. On-line digestion without prior protein denaturation, followed by micro-LC separation and photodiode array detection, was tested with horse-heart cytochrome C and horse skeletal-muscle myoglobin. The complete digestion of 20 pmol μL⁻¹ horse cytochrome C was observed when the average residence time of the protein sample in a 140 cm ×50 μm capillary immobilized enzyme reactor (IMER) was 165 s. Mass spectrometric identification of the injected protein on the basis of the tryptic peptides proved possible. Protein digestion was favorable with respect to reaction time and fragments formed when compared with other on-line and off-line procedures. These results and the easy preparation of this micro-reactor provide possibilities for miniaturized enzyme-reactors for on-line peptide mapping and inhibitor screening.     

Feasibility of treating swine manure in an anaerobic sequencing batch biofilm reactor with mechanical stirring

Anaerobic sequencing batch reactors containing granular or flocculent biomass have been employed successfully in the treatment of piggery wastewater. However, the studies in which these reactors were employed did not focus specifically on accelerating the hydrolysis step, even though the degradation of this chemical oxygen demand (COD) fraction is likely to be the limiting step in many investigations of this type of wastewater. The mechanically stirred anaerobic sequencing batch biofilm reactor offers an alternative for hastening the hydrolysis step, because mechanical agitation can help to speed up the reduction of particle sizes in the fraction of particulate organic matter. In the present study, a 4.5-L reactor was operated at 30°C, with biomass immobilized on cubic polyurethane foam matrices (1 cm of side) and mechanical stirring provided by three flat-blade turbines (6 cm) at agitation rates varying from 0 to 500 rpm. The reactor was operated to treat diluted swine waste, and mechanical stirring efficiently improved degradation of the suspended COD. The operational data indicate that the reactor remained stable during the testing period. After 2 h of operation at 500 rpm, the suspended COD decreased by about 65% (from 1500 to 380 mg/L). Apparent kinetic constants were also calculated by modified first-order expressions.